1. Field of the Invention
This invention relates generally to battery strap and post cast-on machines, to batteries and systems and methods for manufacturing batteries, and more specifically to cast-on-strap (COS) configurations for increased efficiency and reduced energy usage in manufacturing electrical connections between plates within a multi cell battery and between the plates and the battery posts.
2. Background Art
Large batteries, for example, automobile and truck batteries, require special equipment and methods of manufacture. The process for proving electrical connections between the separate plates within the housing of a large battery and between the plate connection and the post that provides connection outside the battery housing is especially critical. Battery failure due to improper connections between plates, shorting within a battery housing, or even catastrophic failure can result in which pressure build-up can cause cell or housing to rupture and create environmental and safety hazards.
Additional considerations arise in providing an efficient and cost effective automated battery manufacturing process while also maintaining product reliability. An ideal process minimizes the material requirements and energy input during production, while simultaneously ensuring that the battery products diminish the risk of failure. While these attributes provide a goal for battery manufacturers to modernize battery production, the many previous attempts to provide for an optimum balance between efficiency and reliability have only provided incremental improvements, without adding significantly to the knowledge in the field.
Casting operations are usually accomplished simultaneously for all the cells of a battery being positioned in a mold having an inverted mirror image, but otherwise oriented as the cells would be in a finished battery cell structure. Stacked cell elements are clamped together with downwardly extending plate lugs adjacent to each other. Plural mold cavities, properly oriented to provide the desired strap shape, may be preheated. Molten metal, usually lead (Pb), or an alloy containing mostly lead, is available in and being continuously being circulated along a channel adjacent to the mold cavities. The lead or molten metal in the channel is preheated usually in a reservoir, usually located below the mold, and then pumped into the channel.
Upon reaching desired conditions, molten metal is pumped into the channel adjacent the mold until the level is raised to overflow weirs disposed between the channel and each mold cavity. The molten metal thus fills the mold cavities, after which the molten metal that has been pumped into the mold to a level above the weir is withdrawn, thereby to recede to a level below the top of the weir. Typically, the level of the molten metal in the channel is maintained between a predetermined set of parameters. When it is desired to overflow the weirs, it is raised to perhaps 12 mm above the level of the channel bottom, and when it is withdrawn, the level is about 6 mm above the channel bottom. Some systems require continuous circulation of the molten metal to and from the reservoir. Others simply raise the level to overflow into the mold cavities, and then pump make up molten metal form the reservoir to the channel.
The source of thermal energy is removed, and the cell plate assemblies, which are clamped in a desired orientation relative to each other, are positioned to immerse a portion of the plate connecting lugs on each plate into the molten mass in an appropriate connector strap mold cavity to provide a molten metal connection between the lugs. The cavities are then chilled, as by flowing water through one or more portions of the mold body, and contact of the chilled water with the mold cavity walls chills the molten lead so as to cause the molten lead to solidify. In most instances, the mold cavities are maintained at a constant temperature by a water jacket that selectively cools the mold cavities when needed, or when directed by thermocouples that monitor the mold temperature. Cooling of the molten metal solidifies the metal around the lugs. After the molded straps and posts solidify sufficiently, they are extracted from the mold with the lugs of the battery cell plates fused or welded to the metal (lead) straps, thereby generating the necessary electrical and mechanical connections therebetween.
For mass production, the above procedures are normally performed in repetitive cycles to provide for commercial efficiency. Cycle time, that is, the time from which the previous completed strap is removed to the time the next one is completed is ideally reduced to a minimum so that the maximum production is achieved in the time available. The efficiencies produced by providing optimal manufacturing parameters result from a number of contributing factors, including reduction of necessary labor, time and materials. It has been found that a substantial portion of the cycle time is involved in heating and cooling portions of the mold body. Reducing to a minimum the time that the lead must be maintained in a molten state reduces the total thermal energy input into the system. Also, if the amount of lead that must be heated to melting and then cooled is minimized, the thermal energy input and the cooling capacity is also reduced, leading to concomitant reductions in cycle time, cost of material, processing costs, etc.
The optimal production parameters provide that the channel walls should not be chilled to such a degree that the molten metal flow is impeded during welding, i.e., solidification or freezing, of the straps, tabs and posts. This allows the molten lead present in the flow channels adjacent the mold assembly to freely flow from the lead channels and into the mold cavity. A minimum degree of precision in the temperature control of the mold assembly is required to maintain the energy input to desirable levels. Nevertheless, cooling of the complete mold, including the weirs, causes the solidification of molten metal in unnecessary locations, as will be explained below. Greater control of localized temperature in the mold assembly is desirable so as to enable cooling of the posts, particularly the terminal posts, at least as rapidly as the less massive strap portions, since slower cooling of the posts would result in mechanically weak terminals.
Mold expense is a significant factor in machines of the type under consideration. It has been difficult to obtain suitable castings in which mold forms can be produced in greater mass quantities without sacrificing one of the other factors that go into the production process and system. This may result in increases of some costs, whether labor, material, energy or other costs, to enable improvements in other points in the process, for example, cycle time, amount of thermal energy input, etc. The variety of cell and terminal arrangements required for large lead-acid batteries has also complicated mold designs, to the detriment of the efficiencies that can be achieved by modifying one or more of the process parameters.
Prior art methods and systems for providing battery strap and post cast-on machines have been disclosed in, for example, U.S. Pat. Nos. 3,718,174 and 3,802,488 issued Feb. 27, 1973, and Apr. 9, 1974, respectively, both of which name as inventors Donald R. Hull and Robert D. Simonton. Described therein are systems and machines, in which stacked battery plates and separators for a plurality of cells making up a lead-acid storage battery have the respective connection lugs for each of the positive and negative plates of each cell interconnected by a cast-on strap. Additionally, an inter-cell connecting or terminal post cast is provided for simultaneous casting in an integral portion of each strap. Conventional designs of this type are described above. The conventional types of molds require the complete mold, including the channel in which the molten metal is circulating to be heated and cooled, when the metal in the mold cavity is solidified. Heating of the complete mold assembly is very inefficient and leads to the waste of thermal energy in the form of heating and cooling the same elements in each cycle, both in terms of unnecessarily increasing cycle time and in terms of the amount of thermal energy expended in each cycle.
U.S. Pat. No. 4,108,417 describes and illustrates a system for pouring molten metal into mold cavities, where the mold portion that contains the mold cavities is partially isolated from the molten metal flow channel. That is, a thermal isolation technique is used wherein the mold cavity walls are isolated from the channel walls so as to provide a quicker cycle time and to permit the mold cavities to be heated quickly just before casting, and cooled when the lugs are placed into the mold cavities.
As shown in FIGS. 1-3, the mold assembly 100 (FIG. 3) includes and isolated portion 10 that is isolated from the flow channels (30, FIG. 3). The separate portion 10 of the mold assembly include the mold cavities 16, some of which may have separate flow chutes 34 (FIG. 3) that communicate with one or more mold cavities for terminal posts or other connections, for example tabs or tombstones, that attach the strap, after it is solidified, to the terminal post of the battery. An isolation member, usually some type of insulating material 15 is interposed between the mold cavity portion 10 and the rest of the mold assembly 100 so as to inhibit flow of thermal energy form the flow channel 30 to the mold cavity portion 10.
Separate flow chutes 34 between one or more of the mold cavities 12 and terminal post cavities 36 are provided for simultaneous casting of the battery terminal posts, thereby avoiding the separate and subsequent welding of terminal posts onto the cast on straps. As background, and to provide for a clearer understanding of the present invention, a more detailed explanation of the conventional methods as taught in various patents is provided.
U.S. Pat. No. 5,776,207 to Tsuchida et al., entitled “Lead acid storage battery and method for making same,” describes and illustrates the use of a heating mechanism including an induction coil to provide instantaneous and accurate supply of thermal energy to the mold. It describes a problem, that is, the surface of the molten lead as it is cooled about the flanges or lugs of the plates does not solidify at a uniform state, and may result in strap “waves” when the lugs are removed from the mold. The induction coil heating is disclosed as providing an improvement in the temperature control to avoid structural problems in the strap configurations. Cooling is described as being provided to the underside surface of the mold by spraying of a coolant, such as water.
As shown in the cross-sectional views of FIGS. 4 and 5, the mold portion 10 provides for each mold cavity 12 to accommodate a plurality of plate lugs 44, 46 that extend downwardly form the separate plates 42. are FIG. 5 shows the plates 44 are each isolated from the adjacent plates 46 by an appropriate semi-permeable electrically insulating material 48, each adjacent plate pair 44, 46 comprising a battery cell. Plates 42, including the isolating material 48, are all clamped together by an appropriate clamp that surrounds the battery cell assembly and maintains the relative positions of the lugs in the desired orientation and position. The lugs 44 for the negative ion plates are adjacent one edge of the plate 42 while an adjacent plate that is positive during normal operation of the battery, so as to attract ions, is at the other edge of the adjacent plate. The mold cavities are appropriately positioned and oriented so that the negative plate lugs 44 all are able to fit into the cavity 12 of a negative lug mold 18 and positive plate lugs 44 all are able to fit into the cavity 12 of a positive lug mold 19 (FIG. 4). The molds are shown schematically to be isolated from the surrounding mold assembly by insulating material 15.
These are generally known methods of providing for isolation of a mold cavity portion of a mold assembly, and reference is made to U.S. Pat. Nos. 4,108,417 and 5,776,207 for teaching the methods. For a background understanding of the molten metal pouring method, and the elevation of the molten metal to a level greater than a gate level so that the molten metal is introduced into the mold cavities 12, reference is made to aforementioned U.S. Pat. No. 4,108,417, which illustrates and describes the generally known methods and supporting elements of a cast-on-strap mold system, such as a reservoir for molten metal, the supply of coolant and means for introducing thermal energy to the mold prior to the casting operation.
U.S. Pat. No. 6,708,753 entitled “Method and apparatus for casting straps onto storage battery plates” generally illustrates and describes the need for a substantial degree of precision of thermal conditions in pouring lead into a mold. It describes an automated process for inserting the lugs of a group of plates into plural mold cavities and injecting lead therein. The patent descries a need to sufficiently cool the mold cavities in order to solidify the lead strap metal prior to battery cell extraction.
U.S. Pat. No. 4,573,514, issued in 1984 and assigned to GNB Batteries Inc., is entitled “Electrically heatable mold and method of casting metal straps” and describes and illustrates a mold and automated method providing for precise control of the temperatures of the mold and lead pour on a continuous basis. Additional features include a tongue-in-groove connection between segments of a mold that have an intervening insulation material and a piston rod that is required to push the molded strap and post construction from out of the mold cavity. A forced air cooling method that cools the strap as soon as the plate tabs are immersed in the molten lead to form a connection between the metal elements, the cooling time being described as about thirty seconds or so. One improvement relates to isolating the cooling of the mold body to only a portion thereof so as to reduce the mass of the mold that requires cooling and subsequent reheating during each cycle. This feature is asserted as providing necessary temperature control for the disclosed process, and also includes a carousel arrangement for providing successive stages in the molding process at various points so that several processes may proceed on a continuous basis.
U.S. Pat. No. 5,836,371, issued in 1998 and assigned to GNB Batteries Inc., is entitled “Method and apparatus for attaching terminal post straps to a battery” and describes and illustrates a mold and method providing for welding the posts of a battery terminal onto the strap after the lugs are connected to each other electrically and mechanically using a plastic insert that is removed prior to the casting of the posts.
U.S. Pat. No. 7,082,985 to Hopwood entitled “Method and apparatus for casting straps onto storage battery plates” illustrates and describes the need for a substantial degree of precision in application of thermal conditions when pouring lead into a mold and further describes a known automated process for inserting the lead into the mold cavity.
What is needed is a mold cavity and process that can quickly and efficiently introduce into a mold cavity and solidify molten metal therein around the lugs of a group of clamped battery cell plates so as to cast on a strap that provides an increase in reliability and reduces the cycle time, as well as significantly reducing the amounts of lead used per cast and the amount of thermal energy that is input into the system for maintaining the metal in a molten state.